"Isn't retirement something to really celebrate?" says Grandy, 65, who did graphic design work and took an early retirement buyout in 2009.

Grandy has a pension, Social Security coverage and retirement savings. But he and his wife, Kathleen, realized that they were withdrawing too much of their savings in the first few years. The Wyandotte, Mich., couple initially treated themselves to eating out more often than they would have in the past. He remembers splurging on some artwork early on, too. If that went on, he said, the savings wouldn't last.

Saving for retirement is one thing; learning how to make that retirement nest egg last 25 years to 30 years or even 40 years is another.

Once you save all that money for retirement, the big question for many baby boomers is what, really, can I afford to spend each year? How much money you need in retirement can depend on whether you have any pension or when you begin collecting Social Security.

Some consider a safe withdrawal rate to be 4 percent each year from a portfolio. But that 4 percent rule is becoming more of a subject of debate in an environment of low-interest rates and high stock market volatility.

"People should not misinterpret it. It's not any kind of guarantee," said Wade Pfau, professor of retirement income at the American College outside Philadelphia.

Pfau warned that the 4 percent is based on the assumption of a fairly aggressive portfolio, which includes stocks. The 4 percent rule would have worked during a 30-year time beginning in 1966, which included a time of high interest rates.

"No one knows what a safe rate will be because returns will depend on future events — which haven't happened and are therefore unknowable," said Marilyn Capelli Dimitroff, director of wealth management and principal at Planning Alternatives in Bloomfield Hills, Mich.

A key question: Is the retiree paying attention to how much he or she is spending? Say a retiree sets up a system to spend 4 percent but then the retiree pays cash for a car, takes out extra money to pay taxes on a cottage, or takes $15,000 or more to pay for a wedding.

Maybe the $50,000 in cash accounts at the beginning of a year drops to $25,000 or less at year end.

"So even though they took out a modest amount from an IRA, in reality they are spending much more than that," Studinger said.

Baby boomer retirees and those four or five years from retirement need to review what they're spending and what adjustments they can make early in the game.

Grandy and his wife put a tighter control on their spending. Now, he's making extra spending money as an artist. The couple focuses on doing things with their nine grandchildren, soon to be 10, instead of lavishing them with gifts, too.

"We don't know how long we're going to live," Grandy said. "We don't know how long we're going to need our money. Who knows the future of anything?"